This invention relates to a probing apparatus and, more particularly, to a wafer prober for use in the examination of electrical characteristics of semiconductor devices formed on a wafer, during the manufacture of such semiconductor devices. In another aspect, the invention is concerned with a probe card to be used with the probing apparatus.
Usually in the field of manufacture of semiconductor devices such as integrated circuits (ICs), and during one of the final stages of the manufacture, the electrical characteristics of respective semiconductor devices, called IC chips, formed on a silicon wafer or the like are examined. Such examination is normally effected prior to cutting the wafer to divide the same into respective IC chips. For the sake of such examination, an integrated-circuit tester, called an IC tester, and a probing apparatus, called a wafer prober, are used. The examination itself of the electrical characteristics of each of the IC chips is carried out actually by the IC tester, and the wafer prober is used in order to establish an electrical connection between the IC tester and each of the IC chips on the wafer. An example of such wafer prober is disclosed in Japanese Laid-Open Utility Model Application, Laid-Open No. 53149/1983.
For the examination, a wafer having formed thereon a number of IC chips, to be tested, is disposed on a wafer stage of the probing apparatus. The wafer stage is movable in the directions of X, Y and Z. On the other hand, a probe card associated with the wafer to be tested is introduced into the probing apparatus and then is held by a holder for rotational displacement in an X-Y plane. The probe card has mounted thereon a plurality of probe needles with tips. The number of the probe needles and the positions of the needle tips correspond respectively to the number and the locations of bonding pads of each IC chip on the wafer. The bonding pad is the area defined on the IC chip to which a bonding wire is to be connected at a later stage during the manufacture of the semiconductor devices.
The probe card and the wafer stage, carrying the wafer, are relatively displaced so that the tips of the probe needles are aligned with the bonding pads of one of the IC chips which is now going to be examined. Subsequently, the wafer stage is moved upwardly in the Z direction until the tips of the probe needles contact the bonding pads of the IC chip, respectively. By thus bringing the needle tips into contact with the bonding pads, the IC chip is electrically connected to the IC tester so that the examination of the electrical characteristics of the IC chip is carried out.
Upon completion of the examination, the wafer stage is moved stepwisely relative to the probe card so that a second IC chip is examined in a similar manner. This is repeated until all the remaining IC chips are examined. Thereafter, the wafer is replaced by a second wafer and similar examination operations are carried out relative to the second wafer.
If the examination is to be made relative to different IC chips having different patterns (and thus having different geometrical arrangements of bonding pads), separate probe cards having different arrangements of probe needles are interchangingly used.
In any event, in order that the probe needles of the probe card are brought into correct contact with the bonding pads of the IC chip, respectively, an accurate alignment must be achieved between the probe card and the wafer (i.e. between the tips of the probe needles and the bonding pads) after they are introduced into the probing apparatus.
The alignment operation in the known type probing apparatuses will now be described. Usually, the alignment is effected through two steps, prealignment (coarse alignment) and final alignment (fine alignment).
The wafer prealignment is a step for coarsely positioning the wafer relative to the probing apparatus or the probe card. As an example, the wafer prealignment is carried out by mechanical positioning. Alternatively, a sensor is used to detect the edge of the wafer to thereby detect the outer periphery of the wafer and the direction of elongation of an orientation flat of the wafer. In accordance with the results of detection, the rotational position of the wafer is adjusted. By the wafer prealignment, the wafer is coarsely positioned so that its orientation flat extends in a desired direction relative to the probing apparatus.
After the wafer prealignment, the final or fine alignment of the wafer relative to the probe card is effected. As for a first wafer, the same is moved manually so that a predetermined one of the IC chips on the first wafer is located under the probe needles. Subsequently, while observing the tips of the probe needles and the bonding pads of the IC chip through a microscope or the like, the probe card is manually displaced in the rotational direction to remove the positional deviation in the rotational direction between the probe card and the wafer (i.e. between the tips of the probe needles and the bonding pads of the IC chip). Then, while continuing the naked-eye observation, the wafer stage is manually displaced minutely in the X and Y directions to accurately align the bonding pads of the IC chip and the tips of the probe needles. When this is achieved, the alignment itself of the first wafer is completed.
In the event that the fine alignment relative to a second wafer, a third wafer, etc. is to be made automatically through the image processing, the following operations are carried out just after the completion of the fine alignment of the first wafer. That is, the first wafer to which the fine alignment is finished is moved so that a predetermined area on the first wafer is located at a position under a TV camera provided for the sake of the image processing. By doing so, the image of the pattern in the predetermined area on the wafer is picked up and the pattern is displayed in a cathode ray tube connected to the TV camera. Subsequently, of the pattern displayed, a desired or predetermined portion is selected and registered as a template. This template is used as a reference for detecting the position of each of the second wafer, the third wafer, etc. during the automatic fine alignment of these wafers.
The first wafer, after completion of the final alignment, is moved to an examination initiating position, and then the examination is carried out by contacting the tips of the probe needles to the bonding pads of the first IC chip, as described in the foregoing. After the examination of the first IC chip is completed, the wafer stage is moved stepwisely in the X and Y directions so that a second IC chip, a third IC chip, etc. of the same wafer are examined.
As for the second wafer to be examined with the use of the same probe card, the prealignment of the second wafer is carried out in the same manner as of the first wafer. On the other hand, the fine alignment of the second wafer can be made automatically by the image processing as described before. For the sake of such automatic fine alignment, the second wafer which has been prealigned is moved so that a predetermined area on the second wafer is located at a position under the TV camera. Next, the image of the pattern in the predetermined area on the wafer is picked up and the pattern is compared with the template which has already been registered during the processing of the first wafer. By this pattern matching, the position of the second wafer relative to the probe card (probe needles) is detected. Any positional deviation between the probe card and the wafer, thus detected, is corrected by controlling the movement of the wafer stage for moving the wafer for the sake of the probing operation of the first IC chip.
In the known type wafer prober, as has been described, the final or fine alignment of the first wafer is effected manually, i.e. by manually changing the positional relation between the tips of the probe needles and the bonding pads of the IC chip while observing them. This is a complicated operation, requiring a prolonged examination time. As described hereinbefore, it is necessary to interchangingly use separate probe cards relative to different wafers having different chip patterns. Every time the probe card is replaced, such complicated fine alignment operation is necessary. Further, due to the physical contact between the tips of the probe needles and the bonding pads, the probe card needs to be demounted from the wafer prober, each time a certain number of wafers are processed, for the sake of cleaning and/or repair of the probe needles. When the cleaned or repaired probe card is introduced again into the wafer prober, the complicated manual fine alignment operation is required again.
On the other hand, in order to permit the prealignment operation, the probing operation, etc. to be effected automatically, it is necessary to preparatively set or specify various data relative to the probing apparatus. Examples of such data are as follows:
(1) Direction of orientation flat . . . It is necessary to specify the direction of elongation of the orientation flat of the wafer to be established by the prealignment operation relative to the probing apparatus or the probe card. By this, the sequence of the probing operations for all the chips on the wafer is determined.
(2) Index stroke . . . It is necessary to specify the index stroke, i.e. the amount of stepwise movement of the wafer stage for the probing operations relative to the IC chips on the wafer. The index stroke is determined by the size of each IC chip, the sequence of the probing operations, etc.
(3) Wafer edge percent . . . The wafer edge percent should be specified in order to determine those of the IC chips formed on a peripheral portion of the wafer that are to be probed or examined. In some cases, such IC chips as having incomplete areas, as compared with the area of the perfect IC chip, are formed on the outer peripheral portion of the wafer. There is a higher possibility that, among these incomplete IC chips, those as having areas not less than a predetermined area are satisfactorily operable as the semiconductor devices. In view of this, the examination of the electrical characteristics is carried out relative to each of those of the IC chips formed on the peripheral portion of the wafer which have areas not less than the predetermined area. The wafer edge percent is the proportion of the above-mentioned predetermined area to the area of the perfect IC chip. By specifying the wafer edge percent, whether or not the examination is to be made relative to an incomplete IC chip is determined.
(4) Alignment parameter . . . For the sake of fine alignment relative to the second wafer, the third wafer, etc., it is necessary to specify the location of the alignment area which is the subject of the pattern matching.
In the known type probing apparatuses, these data or conditions are inputted to the apparatus by manual handling of an operation panel by an operator. This is a complicated and time-consuming operation. Further, the set of these initial conditions is required every time the probe card is replaced by another for a different wafer having different chip pattern. Therefore, it requires exceedingly complicated operations as well as an enormously prolonged examination time. This is of course undesirable.
In order to obviate this problem, it has been proposed to provide the apparatus with a memory and to preparatively store various data in the memory. In such case, however, it is necessary to pay careful attention to the correlation between the wafer to be examined (i.e. the probe card to be used) and the data stored in the memory. Therefore, it still requires a manual operation by an operator each time the probe card is replaced.